1. Technical Field
The present invention relates to a touch panel, and more particularly, to a resistive type touch panel that is configured to distinguish between inadvertent contact with the touch panel and desired selection of a displayed item.
2. Related Art
Touch panels are widely integrated with display surfaces of display devices such as electronic calculators, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescence (EL) devices, and cathode ray tubes (CRTs). Touch panels may be classified into an analog resistive type, a capacitive type, and an EM (Electro-magnetic) type. In general, touch panels are capable of sensing the location on the display surface where a user contacts the display surface with an object such as a pen, a finger, etc. Contact with the display surface results in the generation of a location specific input signal. Based on the information currently displayed, and the particular location where the display surface was touched by the user, the input signal may be converted to input data, such as an input instruction to direct the operation of a computer device. In some applications, a touch screen may be used in place of remote controllers or other input devices that are external to the display device. For example, using a touch panel integrated into a display device, a user may select desired information with a pen or a hand while observing an image displayed by the display device.
Generally, touch panels are provided with upper and lower transparent substrates, each having electrodes formed thereon. The upper and lower transparent substrates may be bonded to each other within a predetermined space. If a surface of the upper transparent substrate is touched at a predetermined point using input means, e.g., a finger, a pen, etc., the electrode formed on the upper transparent substrate electrically connects to the electrode formed on the lower transparent substrate. A voltage, made variable by a resistance value or a capacitance value of the touched point, is then detected and outputted along with a location defined by coordinates of the touched point.
In a capacitive type touch panel, a film having a transparent electrode is formed on an LCD panel. A voltage applied to each corner of the film generates a uniform electric field in the transparent electrode. Thus, a voltage drop is generated when a predetermined point of a display surface is touched with an input means such as finger or conductive stylus, thereby detecting coordinates of the touched point.
FIG. 1 is a schematic view illustrating a resistive type touch panel device according to the related art. As shown in FIG. 1, the touch panel device includes a touch panel 10, a touch panel controller 30, and a system 40. The touch panel 10 outputs a coordinate signal representative of a touched point on a display. The touch panel controller 30 drives the touch panel 10. In addition, the touch panel controller 30 determines coordinates according to the coordinate signal provided by the touch panel 10. The touch panel controller 30 also outputs the value of the coordinates to the system 40. In response to the value of the coordinates from the touch panel controller 30, the system 40 may perform a corresponding command.
The touch panel 10 includes an upper film 12 and a lower film 16. A first transparent conductive layer 14 is formed on a lower surface of the upper film 12, and a second transparent conductive layer 18 is formed on an upper surface of the lower film 16. An adhesive may be used to bond the upper film 12 and the lower film 16. The adhesive may be applied to a peripheral area of the upper and lower films 16 that is a non-touch area. When bonded, a predetermined distance is maintained between the upper film 12 and the lower film 16. The predetermined distance corresponds to a thickness of the adhesive 22.
Prior to bonding, a plurality of dot spacers 20 are formed on the first transparent conductive layer 14 of the upper film 12 or the second transparent conductive layer 18 of the lower film 16. The dot spacers 20 maintain the predetermined distance between the upper film 12 and the lower film 16 during and following bonding. The dot spacers 20 are disposed in a touch area of the upper film 12. As previously discussed, the upper film 12 is subject to touching by a user with, for example a pen or finger.
The upper film 12 may be formed of a transparent film such as a Polyethylene Terephtalate (PET) film. The lower film 16 may also be formed of a transparent film, such as a glass substrate or a plastic substrate of the same material as the upper film 12. The first and second transparent conductive layers 14 and 18 may be formed of a conductive material such as Indium-Tin-Oxide (ITO), Indium-Zinc-Oxide (IZO) and Indium-Tin-Zinc-Oxide (ITZO).
The illustrated touch panel 10 includes an X-electrode bar 15 and a Y-electrode bar 19. The X-electrode bar 15 is in contact with the first transparent conductive layer 14 to apply a voltage to the first transparent conductive layer 14 according to an X-axis direction. The Y-electrode bar 19 is in contact with the second transparent conductive layer 18 to apply a voltage to the second transparent conductive layer 18 according to a Y-axis direction. The X-electrode bar 15 includes a first X-electrode bar 15a for applying a driving voltage Vcc to form a current according to the X-axis direction, and a second X-electrode bar 15b for applying a ground voltage GND. The Y-electrode bar 19 includes a first Y-electrode bar 19a for applying a driving voltage Vcc to form a current according to the Y-axis direction, and a second Y-electrode bar 19b for applying a ground voltage GND.
During operation, when the upper film 12 of the touch panel 10 is touched with a pen or a finger, the first transparent conductive layer 14 is brought into contact with the second transparent conductive layer 18. In response to the contact, a resistance value is varied at the touching point according to a surface resistance of the first and second transparent conductive layers 14 and 18. As a result, the current or the voltage is varied according to the varied resistance value. The varied voltage or current may provide the X-axis coordinate signal. The X-axis coordinate signal is output through the first or second Y-electrode bar 19a or 19b that is in contact with the second transparent conductive layer 18. Alternatively, the varied voltage or current may provide the Y-axis coordinate signal. The Y-axis coordinate signal is output through the first or second X-electrode bar 15a or 15b that is in contact with the first transparent conductive layer 14. In the illustrated example, the touch panel 10 may sequentially output the X-axis coordinate signal and the Y-axis coordinate signal under control of the touch panel controller 30.
Specifically, the driving voltage Vcc and the ground voltage GND may be provided to the X-electrode bar 15 through a first switch 24 included in the touch panel 10. In response to the varied resistance value in the touching point of the first and second transparent conductive layers 14 and 18, the X-axis coordinate signal may be output through the second Y-electrode bar 19b and a second switch 26 included in the touch panel 10. On the other hand, the driving voltage Vcc and the ground voltage GND may be provided to the Y-electrode bar 19 through the first and second switches 24 and 26. In response to the varied resistance value at the touching point of the first and second transparent conductive layers 14 and 18, the Y-axis coordinate signal may be output through the second X-electrode bar 15b. 
The first switch 24 provides the driving voltage Vcc to the first X-electrode bar 15a or the first Y-electrode bar 19a in response to a control signal CS from the touch panel controller 30. The second switch 26 outputs the voltage of the touching point or provides the ground voltage GND to the second X-electrode bar 15b or the second Y-electrode bar 19b in response to the control signal CS of the touch panel controller 30. The touch panel controller 30 detects the X-Y coordinate value of the touching point output from the touch panel 10, and provides the X-Y coordinates to the system 40. As a result, the touch panel controller 30 controls the first and second switches 24 and 26 according to an X-axis coordinate mode and a Y-axis coordinate mode, and provides power source (Vcc and GND) for the touch panel 10.
The touch panel controller 30 includes an analog-digital converter (hereinafter, referred to as ADC) 32, a micom 34 and an interface 36. The ADC 32 converts the X-axis and Y-axis coordinate signals to digital data. The micom 34 detects the coordinate value by combining the X-axis and Y-axis coordinate data. In addition, the micom 34 outputs the coordinate value to the interface 36. The interface 36 provides the coordinate value to the system 40.
When the coordinate values are provided sequentially by the touch panel 10, the ADC 32 converts the X-axis coordinate signal and the Y-axis coordinate signal to digital data, and then outputs the digital data. The micom 34 combines the X-axis coordinate data and the Y-axis coordinate data sequentially provided from the ADC 32 to detect the coordinate value of the touching point. The coordinate value detected by the micom 34 is provided to the system 40 through the interface 36. The micom 34 may also periodically generate the control signal CS to control the operation of the first switch 24 and the second switch 26.
The system 40 detects the coordinate value from the touch panel controller 30 and may perform a corresponding command or an applied program. The system 40 also provides a power source signal and video data for the display. Thus, the touch panel device detects the coordinate value touched by a pen or a finger, transmits the coordinate value to the system 40, and the system 40 performs the corresponding command according to the coordinate value.
However, when the upper film 12 is inadvertently touched with a pen and a finger at the same time by a user, a double touch may be generated. FIG. 2 is an equivalent circuit diagram of the touch panel of FIG. 1. As shown in FIG. 2, if the pen (finger) is touched at a predetermined point on a resistive type touch panel, voltage values for the X-axis and Y-axis of the predetermined point are obtained as follows.X-axis voltage(V)=E×{RX2/(RX1+RX2)}Y-axis voltage(V)=E×{RY2/(RY1+RY2)}
At this time, ‘E’ may be an applied voltage such as 5V or 3.3V, ‘RX1+RX2’ is a resistance of a contact portion with the upper substrate, and ‘RY1+RY2’ is a resistance of a contact portion with the lower substrate.
FIG. 3 is a perspective view of dot spacers disposed on one substrate of the resistive type touch panel according to the related art. As shown in FIG. 3, the plurality of dot spacers 20 are printed and disposed on the upper film 12 or the lower film 16 at fixed intervals in a resistive type touch panel. FIG. 3 shows the dot spacers 20 formed on the lower film 16. The dot spacers 20 are formed of a UV (ultraviolet rays) curing ink type material. The center-to-center distance (Lp) between the dot spacers is ‘Lp=2 mm’. Also, the dot spacer 20 is generally formed as a spherical shape. Typically, the dot spacer 20 is formed of a distorted spherical shape in which a horizontal length ‘Ld’ (FIG. 4) is relatively longer than a vertical height (not illustrated) of the dot spacer 20. For example, the dot spacer 20 has a horizontal length of about 80 μm.
FIG. 4 illustrates an example of a double touch that occurs by touching a pen and a portion of a user's hand on the touch panel at the same time. As shown in FIG. 4, the user may touch the touch panel 10 (upper film 12) with the pen and the hand at the same time when the user inputs letters or draws pictures with the pen. In this case, the double touch is detected on the touch panel 10. That is, two touch points of both a pen touch point (T1) and a hand touch point (T2) are generated on the touch panel 10. The pen touch point (T1) and the hand touch point (T2) may be generated by the touch panel 10 at the same time, or sequentially at a predetermined interval.
If the pen touch point (T1) and the hand touch point (T2) are generated at the same time, the touch panel 10 generates the coordinate signal of a middle point between the pen touch point (T1) and the hand touch point (T2). As a result, the touch panel controller 30 and the system 40 utilize the middle point and thereby generate an error in detecting the pen touch point (T1). If the hand touch point (T2) is generated after the pen touch point (T1) within a predetermined interval, the touch panel 10 generates a first coordinate signal for the pen touch point (T1), and then a second coordinate signal for a middle point between the pen touch point (T1) and the hand touch point (T2). If both the first and second coordinate signals are generated within the predetermined interval, such as a 3.4 ms time period, the touch panel controller 30 detects the coordinate value for the second coordinate signal (the middle point), and then provides the same to the system 40. In response, the system 40 generates an error by detecting the middle point as the pen touch point (T1).
FIG. 5 is an equivalent circuit diagram of the example double touch in the resistive type touch panel of FIG. 4. As shown in FIG. 5, if the double touch of the pen and hand touch points (T1 and T2) are detected together, the middle voltage value of the pen and hand touch points (T1 and T2) is detected as the pen touch point (T1). Electrically, when two points are touched by the pen and the hand, the same resistance R2 is connected between the two points in parallel. For example, supposing that the double touch occurs when 5V (Vcc) is applied to one side of the X-axis or Y-axis electrode bar, and the other side is grounded. At this time, the voltage value of the pen touch point (T1) is,
                    5        ⁢                  (                                    R              ⁢                                                          ⁢              2                        +                          R              ⁢                                                          ⁢              3                                )                                      R          ⁢                                          ⁢          1                +                  R          ⁢                                          ⁢          2                +                  R          ⁢                                          ⁢          3                      ⁢    V    ,                wherein, the relative resistance value is (R2+R3).        
The voltage value of the hand touch point (T2) is,
                    5        ⁢        R        ⁢                                  ⁢        3                              R          ⁢                                          ⁢          1                +                  R          ⁢                                          ⁢          2                +                  R          ⁢                                          ⁢          3                      ⁢    V    ,                wherein, the relative resistance value is R3.        
The voltage value detected by the double touch of the pen and hand touch points is,
                    5        ⁢                  (                                    R              ⁢                                                          ⁢              2                        +                          R              ⁢                                                          ⁢              3                                )                            2        ⁢                  (                                    R              ⁢                                                          ⁢              1                        +                          R              ⁢                                                          ⁢              2                        +                          R              ⁢                                                          ⁢              3                                )                      ⁢    V    ,                wherein, the relative resistance value is (R3+R2/2).        
In this scenario, the voltage signal of the point having the resistance value (R2/2) between the pen and hand touch points (T1 and T2) is transmitted to the touch panel controller 30 and an undesired coordinate value is generated. Accordingly, there is a need for resistive type touch panels capable of differentiating between actual touches and inadvertent touches.